Low cost redundant resolver system

ABSTRACT

A resolver ( 20, 21 ) is provided with redundant excitation windings in which only a single excitation winding (E 1 ) is energized externally. Cross coupling from the externally energized winding (E 1 ) excites the other excitation winding (E 2 ). A control circuit ( 27, 28 ) monitors the excitation of the redundant excitation winding (E 2 ) and switches the excitation to the redundant excitation winding (E 2 ) in the event of a failure of the externally winding (E 1 ).

This appln is a 371 of PCT/US99/19886 filed Sep. 3, 1999 which claimsbenefit of Prov. No. 60/099,029 filed Sep. 3, 1998.

FIELD OF THE INVENTION

This invention relates to resolvers, and more particularly, to animproved resolver with redundant excitation windings.

BACKGROUND ART

Certain specific applications require a shaft position, feedback devicewhich is redundant for safety purposes, but must be inexpensive in orderto be feasible for the application. Typically, two independent feedbackdevices are needed to achieve the redundancy required for theapplication. In order to minimize cost, it is desirable to wind a singleresolver stator lamination stack with two excitation windings and twosets of output windings which are coupled through a single rotor ratherthan providing separate stator lamination stacks and separate rotorpieces. Using conventional winding techniques with two resolver windingson a single core, excited independently, results in cross couplingbetween the redundant windings preventing them from being totallyindependent from one another. This results in a distorted wave form fromthe output windings which causes the decoded feedback information to beinaccurate.

SUMMARY OF THE INVENTION

An object of this invention is the provision of a resolver withredundant windings that minimizes the cross coupling between thewindings while, at the same time, maintaining symmetrical outputsignals.

Briefly, this invention contemplates the provision of a resolver withredundant excitation windings in which only a single excitation windingis energized externally at a given time. Cross coupling from theexternally energized winding induces a voltage in the other excitationwinding. A control circuit monitors the voltage on the redundant windingand switches the excitation to the redundant winding in the event of afailure of the externally excited winding or its excitation source.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, wherein:

FIG. 1 is a end view of a wound resolver with redundant windings.

FIG. 1a is a detail view taken in the region indicated by line 1-1 a inFIG. 1.

FIG. 2 is an end view of another resolver having redundant windings.

FIG. 2a is a detail view taken in the region indicated by line 2 a—2 ain FIG. 2.

FIGS. 3a and 3 b are schematic diagrams of a control circuit accordingto the present invention;

FIG. 4 is a flow chart of the operation of the control circuit of FIGS.3a and 3 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a redundant variable reluctance resolver, having a stator20 and a rotor 21, the stator having sixteen teeth 1-16 on which coilsof several windings to be described are disposed and connected togetherto form windings. FIG. 1a shows coils from excitation windings E1 and E2and sine windings S1 and S2. This redundant resolver has two or moreexcitation windings, in this case E1 and E2, which receive input drivesignals, and sine output windings S1 and S2 and cosine output windingsC1 and C2 which provide output signals. In this example, the firstexcitation winding E1 has coils disposed on all sixteen teeth of thestator 20 and the second excitation winding E2, also with coils disposedon all sixteen teeth 1-16, is redundant. Typically, the redundantexcitation windings E1 and E2 are excited independently. However, unlessthe signals in windings E1 and E2 are closely synchronized with oneanother, cross coupling between the windings E1 and E2 will distort theresolver outputs.

As seen in FIG. 1a, there is a requirement that the windings on eachtooth not be overlapping each other along the length of the tooth 11.FIG. 1a shows only one set of coils for the respective windings, with itbeing understood that the coils on the respective teeth 1-16 areelectrically connected together to form the respective windings. Table 1below shows the arrangement of the coils on the respective teeth 1-16 inFIG. 1 with “cw” meaning the winding of a coil a number of turns in a“clockwise” direction and “ccw” meaning the winding of a coil a numberof turns in a “counterclockwise” direction around a tooth.

TABLE 1 Tooth E1 E2 S1 S2 C1 C2 1 cw cw cw cw — — 2 ccw ccw — — cw cw 3cw cw ccw cw — — 4 ccw ccw — — ccw ccw 5 cw cw cw cw — — 6 ccw ccw — —cw cw 7 cw cw ccw cw — — 8 ccw ccw — — ccw ccw 9 cw cw cw cw — — 10 ccwccw — — cw cw 11 cw cw ccw cw — — 12 ccw ccw — — ccw ccw 13 cw cw cw cw— — 14 ccw ccw — — cw cw 15 cw cw ccw cw — — 16 ccw ccw — — ccw ccw

FIG. 2 shows another resolver with physically separated excitationwindings E1, E2, sine output windings S1, S2 and cosine output windingsC1, C2 wound on a stator 20 a (the rotor is not shown). In thisconfiguration, the first excitation winding E1 is wound only on teeth1-8, while the redundant excitation winding E2 is wound only on teeth9-16, thus placing the windings E1 and E2 in separate 180-degreesections of the stator 20 a, as shown by dividing line 22. Thisarrangement effectively decouples the two windings except in the areawhere winding E1 on tooth 1 is next to winding E2 on tooth 16, and wherewinding E1 on tooth 8 is next to winding E2 on tooth 9. The wave formsof the sine and cosine outputs are distorted as a result of the couplingbetween winding E1 and winding E2 which occurs between teeth 1 and 16 aswell as between teeth 8 and 9, as seen in FIG. 2. If the inputs toexcitation winding E1 and excitation winding E2 were synchronized, thesine and cosine output windings would output symmetrical wave forms.However, in the event of a failure of either excitation winding E1 orexcitation winding E2, the output wave forms would revert back todistorted wave forms resulting in an unusable signal. Therefore, theinvention provides that one excitation winding E1 be excited, and theexcitation winding E2 be excited only in the event of a failure ofexcitation winding E1.

FIG. 2a illustrates the windings on tooth 10 including winding E2 withinputs E2+ and E2−, and the cosine winding C2 with outputs C2+ and C2−.Table 2 below shows the arrangement of the coils on the respective teeth1-16 in FIG. 2.

TABLE 2 Tooth E1 E2 S1 S2 C1 C2 1 cw — cw — — — 2 ccw — — — cw — 3 cw —ccw — — — 4 ccw — — — cw — 5 cw — cw — — — 6 ccw — — — ccw — 7 cw — ccw— — — 8 ccw — — — ccw — 9 — cw — cw — — 10 — ccw — — — cw 11 — cw — ccw— — 12 — ccw — — — ccw 13 — cw — cw — — 14 — ccw — — — cw 15 — ccw — ccw— — 16 — ccw — — — ccw

Referring now to FIGS. 3a and 3 b, the invention is preferably used withthe resolver of FIG. 1. The embodiment in FIG. 2 is less advantageous inthat if either of the excitation windings E1 and E2 fails, a halfsection of the stator is not excited. An excitation driver circuit 23provides drive signals to inputs +E1, −E1 for excitation winding E1. Ananalog-to-digital (A/D) converter section 25 has two inputs connected tomonitor power signals supplied to excitation winding E1. Thisanalog-to-digital (A/D) converter section 25, in turn, is connected to amicroelectronic digital signal processor (DSP) 26, and may, in fact, beintegrated into a single integrated circuit with the DSP 26. The DSP 26has an output connected to control the switching on and off of thedriver circuit 23 at input 23 a.

Similarly, in FIG. 3b, an excitation driver circuit 24 provides drivesignals to inputs +E2, −E2 for excitation winding E2. Theanalog-to-digital (A/D) converter section 28 also has additional inputsconnected to monitor voltages on excitation winding E2. These signalsare converted to digital signals and input to a second DSP 27. The DSP27 has an output connected to control the switching on and off of thedriver circuit 24 at input 24 a.

In accordance with the teachings of this invention only a singleexcitation winding is excited at any one time. Specifically, excitationdriver circuit 23 excites the excitation winding E1 while the voltageinduced in excitation winding E2 from excitation winding E1 is detectedby the DSP 27. Excitation driver circuit 24 does not excite excitationwinding E2 in normal operation. However, when the control circuit 27, 28detects that there is not an induced voltage in excitation winding E2,the logic activates excitation driver circuit 24 to excite winding E2.

FIG. 4 is a flow chart which illustrates the operation of the DSP 27 inexecuting program instructions to establish the functionality of theexcitation windings E1 and E2. Upon power up of drive circuit 23,represented by start block 29, the processor 27 executes instructions toread the voltage induced in winding E2 from winding E1. The processor 27then executes instructions to determine whether there is measurablevoltage induced in winding E2, as a result of power to winding E1, asillustrated by decision block 30. If the result is “Yes,” then theprocessor 27 will proceed to execute instructions to perform otherfunctions as represented by process block 33. If the answer is “No,” itmeans that power to winding E1 has been lost, and the processor 27 willexcite winding E2 by transmitting a control signal to driver circuit 24,as represented by process block 31. The processor will also set an alarmin memory as represented by process block 33. This alarm condition willbe sensed by an appropriate routine and the system will power down orother corrective action will be taken. In the meantime, the processor 27will loop back to perform other functions through execution of block 33.In a further variation of the above-described routine, in the event of a“No” result in decision block 30 that a further signal be sent from theDSP 27, either to the first DSP 26, or directly to driver circuit 23, topositively turn off the driver circuit 23 for winding E1.

Thus, a resolver is provided with redundant excitation windings and acontrol circuit for monitoring these windings and switching power toanother one of the windings, if one of the windings fails.

Having thus described the present invention and its preferredembodiments in detail, it will be readily apparent to those skilled inthe art that further modifications to the invention may be made withoutdeparting from the spirit and scope of the invention as presentlyclaimed.

We claim:
 1. In a resolver having a stator and a rotor, the statorhaving at least a first excitation winding, and first and second outputwindings, an improvement which comprises: a first excitation drivercircuit to drive said first excitation winding; a second excitationwinding disposed on the stator; a second excitation driver circuit todrive said second excitation winding; a control circuit for sensing aninduced voltage in said second excitation winding induced by theexcitation of the first excitation winding; and wherein said controlcircuit responds to a lack of induced voltage in the second excitationwinding to switch on the second excitation driver circuit.
 2. Theimprovement of claim 1, wherein said control circuit comprises amicroelectronic processor for executing program instructions to sense aninduced voltage in said second excitation winding and to controlswitching of the second excitation driver circuit.
 3. The improvement ofclaim 1, wherein the first excitation winding and the second excitationwinding are disposed on each of the teeth of the stator.
 4. Theimprovement of claim 1, wherein the output windings of the resolverinclude at least one sine winding and at least one cosine winding. 5.The improvement of claim 1, wherein the output windings of the resolverinclude at least two sine windings and at least two cosine windings. 6.The improvement of claim 5, wherein the sine windings and cosinewindings are disposed on the stator in the sequence provided in Table 1.